Tuesday, July 08, 2025

Algae of polar origin may impact tropical ocean biogeochemistry, food webs

Ocean-Land-Atmosphere Research (OLAR)

Graphical Abstract for “Unexpected Abundance and Gene Expression of Polarella from a Tropical Oxygen Deficient Zone” — image:
*Polarella* has only been isolated from polar regions, though through -omics techniques, we have been able to identify the genera in a tropical oxygen deficient zone. Our data suggests that as oxygen and light declines, *Polarella* shifts from a phototrophic lifestyle (green) to potential heterotrophy (orange). At depths where oxygen is depleted and light level extremely low, *Polarella* upregulates genes involved in the uptake of both inorganic and organic nutrients and stress response.
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Credit: Birch Maxwell Lazo-Murphy designed the concept image and was finalized by the OLAR editorial office/graphic design team

A tiny single-celled organism may have a big impact on how the world’s basic chemical building blocks cycle between living things and the non-living environment. Called Polarella, the algal genus was thought to be restricted to polar cap regions of Earth, but a team has revealed that it is abundant and influential in the Eastern Tropical North Pacific Ocean off the coast of Mexico.

The researchers, based at the University of South Carolina (USC), published their findings on May 26 in Ocean-Land-Atmosphere Research.

Polarella is a type of dinoflagellate that makes up a major portion of marine microbial communities and contributes significantly to global primary production, said first author Birch Maxwell Lazo-Murphy, a graduate student pursuing a Ph.D. in marine science in the laboratory of Xuefeng “Nick” Peng, the corresponding author and an assistant professor of in USC’s School of Earth, Ocean, and Environment.

“Understanding the roles of free-living dinoflagellates — as opposed to those that live in symbiosis with other organisms — in dynamic environments is critical, as these habitats often harbor high microbial diversity and niche differentiation,” Lazo-Murphy said. “Gaining a deeper insight into these environments will enable more accurate predictions of how these globally important groups will respond to environmental changes.”

One such dynamic environment in marine systems are oxygen-deficient zones (ODZs), where oxygen levels are so depleted that oxygen often can’t be detected even by state-of-the-art sensors. This results from a process called remineralization, which involves living matter decaying into its basic chemical building blocks. According to Lazo-Murphy and Peng, these zones account for less than 1% of the ocean area on Earth, yet they are responsible for losing 33% of biologically available nitrogen — which is critical for plant growth, human health and more — across the globe.

“ODZs have been expanding in size in part due to anthropogenic warming, so the role of ODZs and their respective microbial communities in global nutrient cycling is becoming increasingly important,” Peng said.

To better understand the specific microbial communities in these areas, including how they respond to change and potentially impact nutrient cycling, the researchers used a technique called metatranscriptomics. They collected seawater samples from the oxygen-rich surface, mid-depths and oxygen-depleted depths of the Eastern Tropical North Pacific Ocean, which houses the world’s largest ODZ. They extracted and sequenced genetic material, from which they identified the specific organisms present in each sample.

“We found unexpectedly high relative contribution of Polarella, which is thought to have bipolar distribution, to the microbial communities in the Eastern Tropical North Pacific Ocean,” Lazo-Murphy said. “Once we established their abundance, we set out to understand the functions and gene expressions of Polarella, as well as their impacts on the nutrient cycles, in the ODZ.”

Further analysis revealed increased expression of stress response genes in Polarella, ranging from the lowest stress in surface samples to the highest in samples from oxygen-depleted depths. The researchers also found that the closer to the surface, genes for photosynthesis — converting sunlight into energy — were more highly expressed. In addition, they found that, while the overall gene expression was low for Polarella from low-oxygen or oxygen-free areas, the genes involved in transporting organic and inorganic nutrients were more highly expressed. Lazo-Murphy said this suggests that Polarella has an opportunistic lifestyle, taking advantage of available resources wherever it exists.

“Collectively, these findings suggest that Polarella thrives beyond polar regions and likely plays a more significant ecological and biogeochemical role in the ocean than previously recognized,” Lazo-Murphy said.

The Simons Foundation Postdoctoral Fellowship in Marine Microbiology and the Simons Early Career Investigator in Aquatic Microbial Ecology and Evolution Award to Peng supported this research.

Journal

Ocean-Land-Atmosphere Research

DOI

10.34133/olar.0094

Method of Research

Data/statistical analysis

Article Title

Unexpected Abundance and Gene Expression of Polarella from a Tropical Oxygen Deficient Zone

Children under three learn new words even when speakers wear masks

A study from the UAB suggests that infants’ optimal attention strategy for acquiring new vocabulary involves following the speaker's gaze and focusing on the object, but does not depend on focusing on mouth or eye movements.

Universitat Autonoma de Barcelona

Children under three learn new words even when speakers wear masks — image:
Stills from the videos shown to the children with a person teaching them the names of new objects in the three experimental conditions. Credits: Joan Birulés and Mathilde Fort.
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Credit: Joan Birulés and Mathilde Fort

A research team from the Universitat Autònoma de Barcelona (UAB) and the University of Grenoble Alpes - Centre National de la Recherche Scientifique (CNRS) has shown that from the age of two, children can learn new words even when the person talking to them has their mouth or eyes covered. According to this study, vocabulary learning at this age is associated with following the speaker's gaze and focusing on the object shown to them when the new word is pronounced, but does not depend on selective attention to the speaker's mouth or eyes.

These results offer reassurance about the use of facemasks and their potential impact on the language development of young children, a concern raised by families and childcare professionals during the COVID pandemic.

The study, published in the journal Developmental Psychology, is the first to show that, from the age of two, children are able to learn new vocabulary, i.e., to create associations between words and unfamiliar objects, after a brief audiovisual interaction. At the same time, it underlines the importance of social reference - looking at the speaker for reinforcement of their response - and attentional control in learning new words.

Exploring how children's attention affects vocabulary learning

Both gaze following skills and selective attention to a speaker’s mouth have been associated with the dramatic improvement in word acquisition that occurs during the second year—a phenomenon known as the vocabulary boost. This has led some experts to propose that both attention strategies may play a key role in the lexical development of infants. However, until now, no cause-effect relationship has been found to validate this hypothesis.

"Previous studies suggested that looking at the speaker's mouth facilitates children’s speech processing and, specifically, the understanding and memorisation of new words, thanks to the visual cues provided by mouth movements. If so, wearing a mask should hinder the learning of new words", explains Joan Birulés, researcher at the Department of Basic, Developmental and Educational Psychology at the UAB and first author of the study.

To investigate this further, the research team recorded the gaze of French children aged between 17 and 42 months while they participated in a word learning task in one of three situations: with the speaker's face completely visible, with their eyes covered with dark glasses, or with their mouth covered by a surgical mask. In the task, infants were shown a screen with a speaker and an object on both sides. The speaker uttered a monosyllabic word six times and, simultaneously, on two occasions shifted the gaze to the object associated with the word.

Results showed that children learned new words starting at 24 months and, surprisingly, that this learning was not affected by the glasses or mask. Better word learning was correlated with gaze-following behaviour—moving the gaze towards the object and alternating between the speaker's face and the object—across all ages and conditions. While masking the eyes or mouth modified attention patterns and made infants focus more on the uncovered facial regions, this manipulation did not affect their ability to form new associations between the new word label and the object.

“The results indicate that children's optimal attention strategy is based on social understanding and visual exploration of the object, and that audiovisual information from the speaker's mouth is not an essential mechanism for rapidly establishing new associations between words and their meaning, at least in typically developing children and in learning or fast mapping contexts”, the researcher adds.

In the bare-face situation, moreover, children preferred to look at the speaker's eyes rather than at the mouth, contrary to previous studies in children exploring the interlocutor's face. This leads the research team to consider that children aged 1.5-3 years are already able to control visual attention in a flexible way, adjusting selective attention between the interlocutor’s eyes and mouth, depending on the task requirements.

Strategy to enhance word learning

Based on the results of the study, the researchers suggest that an effective strategy to enhance word learning in infancy would be to encourage deeper exploration of the object in question, along with rapid visual shifts between the object and the speaker's face.

However, they do not rule out that attention to the speaker's mouth could be beneficial in more complex speech-processing situations, such as in children with hearing impairments, language disorders, or autism spectrum disorders. “In such cases, visual cues from the mouth could become essential, a question we are currently exploring in collaboration with health centres in Grenoble”, says Joan Birulés.

Stills from the videos shown to the children with a person teaching them the names of new objects in the three experimental conditions. Credits: Joan Birulés and Mathilde Fort.

Credit

Joan Birulés and Mathilde Fort

Visual description of the word learning task used in the study. Credits: Joan Birulés and Mathilde Fort.

Credit

Joan Birulés and Mathilde Fort.